Molecular mechanisms of RET activation in human neoplasia

Global research landscape and trends of papillary thyroid cancer therapy: a bibliometric analysis

Background

Papillary thyroid cancer (PTC) is the most common endocrine malignancy worldwide. The treatment of PTC has attracted extensive attention and discussion from the public and scholars. However, no article has systematically assessed the related literature. Therefore, we conducted a bibliometric and knowledge map analysis to reveal the dynamic scientific developments in the PTC therapy field.

Methods

We retrieved publications related to PTC therapy from the Web of Scientific Core Collection (WoSCC) on May 1, 2023. The bibliometric package in R software, VOSviewer and CiteSpace software were used to analyze countries/regions, institutions, journals, authors, references, and keywords. Then, we systematized and summarized the research landscape, global trends and hot topics of research.

Results

This bibliometric analysis spanned from 2012 to 2022 and involved 18,501 authors affiliated with 3,426 institutions across 87 countries/regions, resulting in the publication of 3,954 papers in 860 academic journals. Notably, the number of publications and citations related to PTC therapy research has exhibited a steady increase over the past decade. China and the United States have emerged as leading contributors in terms of publication count, with the United States also being the most cited country. Furthermore, among the top 10 institutions with the highest number of published papers, half were located in China. Among the journals, Thyroid is ranked first in terms of total publications and citations. The most productive individual author was Miyauchi Akira. While previous research primarily focused on surgery and radioactive iodine therapy, the increasing emphasis on health awareness and advancements in medical technology have led to the emergence of active surveillance, thermal ablation, and genomic analysis as prominent areas of research.

Conclusion

In conclusion, this comprehensive and quantitative bibliometric analysis elucidates the research trends and hotspots within PTC therapy, drawing from a substantial body of publications. This study provides valuable insights into the historical and current landscape of PTC therapy research while also offering guidance for future research directions. This study serves as a valuable resource for researchers and practitioners seeking new avenues of exploration in the field.

ALK and RET Inhibitors Promote HLA Class I Antigen Presentation and Unmask New Antigens within the Tumor Immunopeptidome

T-cell immunotherapies are often thwarted by the limited presentation of tumor-specific antigens abetted by the downregulation of human leukocyte antigen (HLA). We showed that drugs inhibiting ALK and RET produced dose-related increases in cell-surface HLA in tumor cells bearing these mutated kinases in vitro and in vivo, as well as elevated transcript and protein expression of HLA and other antigen-processing machinery. Subsequent analysis of HLA-presented peptides after ALK and RET inhibitor treatment identified large changes in the immunopeptidome with the appearance of hundreds of new antigens, including T-cell epitopes associated with impaired peptide processing (TEIPP) peptides. ALK inhibition additionally decreased PD-L1 levels by 75%. Therefore, these oncogenes may enhance cancer formation by allowing tumors to evade the immune system by downregulating HLA expression. Altogether, RET and ALK inhibitors could enhance T-cell-based immunotherapies by upregulating HLA, decreasing checkpoint blockade ligands, and revealing new, immunogenic, cancer-associated antigens.

Oncocytic Variant of Medullary Thyroid Carcinoma: A Rare Case of Sporadic Multifocal and Bilateral RET Wild-Type Neoplasm with Revision of the Literature

Oncocytic variant of medullary thyroid carcinoma (OV-MTC) is a very unusual entity, up to date only 17 cases have been reported in the literature. MTC is a neuro-endocrine malignancy arising from the para-follicular C cells of the thyroid gland. It generally has a slight female predominance and appears as a single lesion. However in the Multiple Endocrine Neoplasia Syndrome 2, linked to the point mutation of RET oncogene, multifocal MTCs may also occur. Herein, we report the case of a 75 years old man with a rare form of sporadic multifocal and bilateral OV-MTC expressing wild-type RET gene. The histological and molecular features of this rare entity are presented and discussed with revision of the pertinent literature.

Lenvatinib and other tyrosine kinase inhibitors for the treatment of radioiodine refractory, advanced, and progressive thyroid cancer

Lenvatinib is a small oral molecule able to inhibit three of the extracellular and intracellular molecules involved in the modulation of angiogenesis and lymphangiogenesis: vascular endothelial growth factor receptor 1–3, fibroblast growth factor receptor 1–4, and platelet-derived growth factor receptor alpha. Since it is also able to inhibit the REarranged during Transfection oncogene and the protooncogene c-KIT, this drug can also be used to control tumor cell proliferation. The maximum tolerated dose, as demonstrated in Phase I studies, is 25 mg daily. The drug is rapidly absorbed with maximum concentrations achieved within 3 and 5 hours after administration in fasting and nonfasting treated patients, respectively. The most common adverse events, reported in Phase I study and confirmed in the subsequent Phase II and III studies, are hypertension, proteinuria, and gastrointestinal symptoms such as nausea, diarrhea, and stomatitis. In Phase I studies, efficacy of lenvatinib in solid tumors was demonstrated, and these encouraging results have led to the development of a Phase II study using lenvatinib in advance radioiodine-refractory differentiated thyroid cancer (DTCs) patients. Since an overall response rate of 50% was reported, this study also confirmed the efficacy of lenvatinib in DTCs patients with an acceptable toxicity profile. Recently, a Phase III study in patients with DTCs (SELECT study) demonstrated the lenvatinib efficacy in prolonging progression-free survival with respect to the placebo (18.3 vs 3.6 months; P<0.001). Although there was no statistically significant difference in the overall survival of the entire group, this result was observed when the analysis was restricted to both the follicular histotype and the group of senior patients (>65 years). The study confirmed that the most common side effects of this drug are hypertension, diarrhea, decreased appetite, weight loss, nausea, and proteinuria. In this review, we report the results of the main studies on lenvatinib efficacy in patients with advanced and progressive thyroid cancer, mainly in DTCs but also in medullary and anaplastic thyroid cancer. We also compared the efficacy of lenvatinib with that of other tyrosine kinase inhibitors, mainly sorafenib, already tested in the same type of patient population.

Intracellular signal transduction and modification of the tumor microenvironment induced by RET/PTCs in papillary thyroid carcinoma

RET gene rearrangements (RET/PTCs) represent together with BRAF point mutations the two major groups of mutations involved in papillary thyroid carcinoma (PTC) initiation and progression. In this review, we will examine the mechanisms involved in RET/PTC-induced thyroid cell transformation. In detail, we will summarize the data on the molecular mechanisms involved in RET/PTC formation and in its function as a dominant oncogene, on the activated signal transduction pathways and on the induced gene expression modifications. Moreover, we will report on the effects of RET/PTCs on the tumor microenvironment. Finally, a short review of the literature on RET/PTC prognostic significance will be presented.

Risk profiles and penetrance estimations in multiple endocrine neoplasia type 2A caused by germline RET mutations located in exon 10

Multiple endocrine neoplasia type 2 is characterized by germline mutations in RET. For exon 10, comprehensive molecular and corresponding phenotypic data are scarce. The International RET Exon 10 Consortium, comprising 27 centers from 15 countries, analyzed patients with RET exon 10 mutations for clinical-risk profiles. Presentation, age-dependent penetrance, and stage at presentation of medullary thyroid carcinoma (MTC), pheochromocytoma, and hyperparathyroidism were studied. A total of 340 subjects from 103 families, age 4-86, were registered. There were 21 distinct single nucleotide germline mutations located in codons 609 (45 subjects), 611 (50), 618 (94), and 620 (151). MTC was present in 263 registrants, pheochromocytoma in 54, and hyperparathyroidism in 8 subjects. Of the patients with MTC, 53% were detected when asymptomatic, and among those with pheochromocytoma, 54%. Penetrance for MTC was 4% by age 10, 25% by 25, and 80% by 50. Codon-associated penetrance by age 50 ranged from 60% (codon 611) to 86% (620). More advanced stage and increasing risk of metastases correlated with mutation in codon position (609→620) near the juxtamembrane domain. Our data provide rigorous bases for timing of premorbid diagnosis and personalized treatment/prophylactic procedure decisions depending on specific RET exon 10 codons affected.

XL184 (cabozantinib) for medullary thyroid carcinoma

INTRODUCTION

Intrathyroidal medullary thyroid carcinoma (MTC) can generally be cured by surgery, but distant metastases are often already present at diagnosis.Currently, there is no effective treatment for metastatic MTC. In these cases, consensus treatment guidelines explicitly recommend new experimental drugs. Several kinase inhibitors are now being tested for treatment of MTC in clinical trials and XL184, an oral, small-molecule multi-kinase inhibitor, seems to be one of the most promising of these compounds.

AREAS COVERED

We review preliminary data on the safety and efficacy of XL184 in metastatic MTC based on an extensive search of the literature, which included published articles, abstracts and website information. In particular,the review focuses on the rationale for using XL184 in advanced MTC. The compound has been specifically designed to target multiple signaling pathways,and this is expected to produce synergistic antitumor effects superior to those achieved by single-kinase inhibition. Preliminary results from the Phase I study of XL184 seem to support this hypothesis.

EXPERT OPINION

Multiple receptor tyrosine kinases (RTKs) are concomitantly activated in the same tumor. The blockade of a single RTK may engage compensatory signaling that maintains cell growth. Targeting multiple kinases might overcome both intrinsic and acquired resistance to antitumoral drugs.

Carcinoma de tireóide na infância e adolescência

Aproximadamente 10% das neoplasias de tireóide aparecem abaixo dos 21 anos e representam 3% das neoplasias da infância, com predomínio em meninas (2F:1M). São papilíferos em 90% casos e mais freqüentemente bilaterais, multifocais e de maior dimensão. Invasão de cápsula e metástases ganglionar ou pulmonar são mais freqüentes que no adulto. O efeito carcinogênico da radiação é especialmente importante na criança pré-púbere. Em 5% dos casos de PTC existe história familial. Genes como o RET/PTC, RAS e BRAF estão habitualmente envolvidos na gênese do processo. A apresentação clínica pode ser nódulo cervical (90% casos) sem que represente um fator de pior prognóstico. O US e a PAAF são procedimentos diagnósticos valiosos. O tratamento deve ser cirúrgico (tireoidectomia total com esvaziamento ganglionar) seguido de PCI e radioterapia ablativa. A substituição com L-tiroxina deve objetivar a supressão crônica do TSH. O prognóstico ao longo prazo é melhor que no adulto. A quantificação da Tg plasmática também é útil na detecção da doença residual.

Polimorfismos genéticos: implicações na patogênese do carcinoma medular de tireóide

O carcinoma medular de tireóide (CMT) é uma neoplasia maligna rara, ocorrendo na forma esporádica ou hereditária. Mutações germinativas no proto-oncogene RET são responsáveis pelo CMT hereditário. No entanto, a maioria dos casos de CMT ocorre em indivíduos sem história familiar, na qual a patogênese da doença ainda é pouco compreendida. Os polimorfismos do gene RET são descritos na população geral assim como em pacientes com CMT. Embora estas variações alélicas aparentemente não confiram qualquer atividade transformadora no receptor RET, estudos sugerem que essas alterações genéticas podem modificar a suscetibilidade à doença e o fenótipo clínico em pacientes com CMT esporádico ou hereditário. Uma maior freqüência dos polimorfismos localizados nos exons 11 (G691S), 13 (L769L), 14 (S836S) e 15 (S904) é descrita em pacientes com CMT provenientes de países americanos e europeus. Na presente revisão, analisamos criticamente os resultados obtidos nos diferentes estudos e descrevemos a freqüência dos polimorfismos do RET em pacientes brasileiros com CMT esporádico.

In search of tumor suppressing functions of menin

Human hereditary tumor syndromes serve as an ideal model for studying molecular pathways regulating tumorigenesis. Multiple endocrine neoplasia type 1 (MEN1), a human familial tumor syndrome, results from mutations in the Men1 gene. Men1 encodes a novel tumor suppressor, menin, of unknown biochemical function. Recently, significant progress has been made in identifying menin as a regulator of gene transcription, cell proliferation, apoptosis, and genome stability, leading to a new model of understanding menin's tumor-suppressing function. These findings suggest that menin's diverse functions depend on its association with chromatin and its control over gene transcription. This knowledge will likely be translated into new strategies to improve therapeutic interventions against MEN1 and other related cancers.

RET is constitutively activated by novel tandem mutations that alter the active site resulting in multiple endocrine neoplasia type 2B

Constitutive activation of the RET receptor tyrosine kinase underlies the genesis and progression of multiple endocrine neoplasia type 2 (MEN 2), a dominantly inherited cancer predisposition. Importantly, although kinase activation represents a common theme in neoplasias, not all activating mutations are functionally equivalent. Consistent with this, we ascertained a patient with classical features of MEN 2B, but lacking either of the classical mutations in RET (M918T or A883F). Instead, the patient harbors a novel pair of germ line missense mutations in cis at codons 804 and 805. We evaluated the potential physiochemical effects of these substitutions in silico, predicting both to be moderately deleterious in isolation, but severely deleterious in combination. Consistent with this postulate, we show that the identified tandem mutations (V804M/E805K) are biologically active, transforming cells in culture and that their transforming capacity in combination is distinctly synergistic. Furthermore, the V804M/E805K tandem lesion confers resistance to the small molecule receptor tyrosine kinase inhibitor, PP1, suggesting a mode of action distinct from that known for classical MEN 2B mutations. To address this question, we used homology molecular modeling in silico to model the active site of RET. We predict that RET804 constitutes a critical gatekeeper residue that, when mutated in combination with RET805, induces a conformational change in the hinge region that locks the active site in a position permissive for ATP hydrolysis. Our findings have implications both in the clinic and in the successful development of novel kinase-targeted anticancer drugs.

A Novel Activating Mutation in the RET Tyrosine Kinase Domain Mediates Neoplastic Transformation

We report the finding of a novel missense mutation at codon 833 in the tyrosine kinase of the RET proto-oncogene in a patient with a carcinoma of the thyroid. In vitro experiments demonstrate that the R833C mutation induces transformed foci only when present in the long 3′ splice isoform and, in keeping with a model in which the receptor has to dimerize to be completely activated, glial cell line-derived neurotrophic factor stimulation leads the RETR833C receptor to a higher level of activation. Tyrosine kinase assays show that the RETR833C long isoform has weak intrinsic kinase activity and phosphorylation of an exogenous substrate is not elevated even in the presence of glial cell line-derived neurotrophic factor. Furthermore, the R833C mutation is capable of sustaining the transformed phenotype in vivo but does not confer upon the transformed cells the ability to degrade the basement membrane in a manner analogous to metastasis. Our functional characterization of the R833C substitution suggests that, like the V804M and S891A mutations, this tyrosine kinase mutation confers a weak activating potential upon RET. This is the first report demonstrating that the introduction of an intracellular cysteine can activate RET. However, this does not occur via dimerization in a manner analogous to the extracellular cysteine mutants.

Neoplasia endócrina múltipla tipo 2

O termo neoplasia endócrina múltipla tipo 2 (NEM 2) foi sugerido em 1968, por Steiner e cols., para diferenciar a síndrome clínica caracterizada pela presença de carcinoma medular de tireóide (CMT), feocromocitoma e hiperparatireoidismo, então denominada síndrome de Sipple, da síndrome de Wermer ou NEM tipo 1, que acomete as glândulas paratireóides, pâncreas e hipófise. Sizemore e cols. (1974) complementaram a diferenciação através da classificação da NEM 2 em 2 subgupos: pacientes com CMT, feocromocitoma, hiperparatireoidismo e aparência normal (NEM 2A) e pacientes sem acometimento das paratireóides e fenótipo caracterizado por ganglioneuromatose intestinal e hábitos marfanóides (NEM 2B). CMT é usualmente o primeiro tumor a ser diagnosticado. O diagnóstico do CMT determina que seja avaliada a extensão da doença e rastreamento do feocromocitoma e hiperparatireoidismo. O diagnóstico de CMT esporádico ou hereditário é realizado através da análise molecular do proto-oncogene RET. Neste artigo são discutidos os aspectos fisiopatológicos, as anormalidades genéticas e os aspectos clínicos da NEM 2. A abordagem diagnóstica e terapêutica nos indivíduos afetados, carreadores assintomáticos e familiares em risco também são discutidos. Os avanços relacionados ao rastreamento genético e intervenção precoce permitiram uma melhoria no prognóstico a longo prazo. No entanto, ainda não dispomos de tratamento eficaz para doença metastática.

Hereditary hormone excess: genes, molecular pathways, and syndromes

Hereditary origin of a tumor helps toward early discovery of its mutated gene; for example, it supports the compilation of a DNA panel from index cases to identify that gene by finding mutations in it. The gene for a hereditary tumor may contribute also to common tumors. For some syndromes, such as hereditary paraganglioma, several genes can cause a similar syndrome. For other syndromes, such as multiple endocrine neoplasia 2, one gene supports variants of a syndrome. Onset usually begins earlier and in more locations with hereditary than sporadic tumors. Mono- or oligoclonal ("clonal") tumor usually implies a postnatal delay, albeit less delay than for sporadic tumor, to onset and potential for cancer. Hormone excess from a polyclonal tissue shows onset at birth and no benefit from subtotal ablation of the secreting organ. Genes can cause neoplasms through stepwise loss of function, gain of function, or combinations of these. Polyclonal hormonal excess reflects abnormal gene dosage or effect, such as activation or haploinsufficiency. Polyclonal hyperplasia can cause the main endpoint of clinical expression in some syndromes or can be a precursor to clonal progression in others. Gene discovery is usually the first step toward clarifying the molecule and pathway mutated in a syndrome. Most mutated pathways in hormone excess states are only partly understood. The bases for tissue specificity of hormone excess syndromes are usually uncertain. In a few syndromes, tissue selectivity arises from mutation in the open reading frame of a regulatory gene (CASR, TSHR) with selective expression driven by its promoter. Polyclonal excess of a hormone is usually from a defect in the sensor system for an extracellular ligand (e.g., calcium, glucose, TSH). The final connections of any of these polyclonal or clonal pathways to hormone secretion have not been identified. In many cases, monoclonal proliferation causes hormone excess, probably as a secondary consequence of accumulation of cells with coincidental hormone-secretory ability.

Penetrance and clinical manifestations of non-hotspot germline RET mutation, C630R, in a family with medullary thyroid carcinoma

Germline mutations in specific hot spot-codons of the RET proto-oncogene are associated with multiple endocrine neoplasia type 2 (MEN 2). Clinical RET gene testing has been routine for the last 10 years in some countries. In Argentina, RET testing excluding MEN 2B was always reported with a mutation at codon 634, with one exception: we described a novel mutation T > C transition at codon 630 (C630R), the family to which we extend the study in the present report. This family comprised 29 members in four generations including 6 individuals affected with medullary thyroid cancer (MTC), positive for the C630R mutation and normal adrenaline/ noradrenaline and ionized calcium/parathyroid hormone levels. Two asymptomatic mutation carriers aged 5 and 11 years underwent total thyroidectomy. The histopathologic examination showed C-cell hyperplasia and microcarcinoma foci, while preoperative basal calcitonins were normal for both. Our report emphasizes the importance of testing for non-hot spot RET mutations in apparently mutation negative MEN 2 families. Furthermore, it would appear that C630R mirrors C634R in penetrance (100% in this family) and in early age of onset of MTC, although paradoxically, no pheochromocytomas and hyperparathyroidism have developed. In addition to recommending RET testing before 5 years of age; we also can postulate that codon 630 may be the key point along the extracellular domain, important in the tissue-specific penetrance.

Carcinoma medular de tireóide: aspectos moleculares, clínico-oncológicos e terapêuticos

O carcinoma medular de tireóide (CMT) pode ocorrer na forma esporádica ou familiar. O CMT hereditário é parte das síndromes de neoplasia endócrina múltipla (NEM) 2A e 2B, carcinoma medular de tireóide familiar (CMTF) ou outras formas. Mutações de linhagem germinativa do proto-oncogene RET causam a forma hereditária da neoplasia e os testes genéticos atualmente disponíveis formam a base para o manejo adequado da hereditariedade do tumor, visto que o diagnóstico precoce melhora significativamente o prognóstico no indivíduo afetado e nos carreadores. Nos últimos anos, vários estudos têm demonstrado uma correlação entre mutações codon-específica do RET e os diferentes fenótipos da NEM 2A, que pode, em parte, ser explicada por diferenças na intensidade da indução da dimerização do receptor. No presente artigo, revisamos os avanços nos mecanismos moleculares, diagnóstico e tratamento, bem como relatamos a nossa experiência no manejo dessa forma rara de neoplasia tireoidiana.

Identification of a surface for binding to the GDNF-GFR alpha 1 complex in the first cadherin-like domain of RET

The RET receptor tyrosine kinase is activated by binding to a ligand complex formed by a member of the glial cell line-derived neurotrophic factor (GDNF) family of neurotrophic factors bound to its cognate GDNF-family receptor-alpha (GFR alpha) glycosylphosphatidylinositol-linked co-receptor. Molecular modeling studies of the extracellular domain of RET (RETECD) have revealed the existence of four cadherin-like domains (CLD1-4) followed by a cysteine-rich domain. Cross-linking experiments have indicated that the RETECD makes direct contacts with both the GDNF ligand and GFR alpha 1 molecule in the complex, although it has low or no detectable affinity for either component alone. We have exploited sequence and functional divergences between the ectodomains of mammalian and amphibian RET molecules to map binding determinants in the human RETECD responsible for its interaction with the GDNF-GFR alpha 1 complex by homologue-scanning mutagenesis. We found that Xenopus RETECD was unable to bind to GDNF-GFR alpha-1 or neurturin (NTN)-GFR alpha-2 complexes of mammalian origin. However, a chimeric molecule containing CLD1, -2, and -3 from human RETECD, but neither domain alone, had similar binding activity as compared with wild type human RETECD, suggesting the existence of an extended ligand binding surface within the three N-terminal cadherin-like domains of human RETECD. Subsequent loss-of-function experiments at higher resolution identified three small subsets of residues, mapping on the same face of the molecular model of RET CLD1, that were required for the interaction of human RETECD with the GDNF-GFR alpha 1 complex. Additional experiments demonstrated that N-linked glycosylation of human RETECD was not required for ligand binding. Based on these observations, we propose a model for the assembly and architecture of the GDNF-GFR alpha 1-RET complex.

Molecular modeling of the extracellular domain of the RET receptor tyrosine kinase reveals multiple cadherin-like domains and a calcium-binding site

Using bioinformatic tools, mutagenesis, and binding studies, we have investigated the structural organization of the extracellular region of the RET receptor tyrosine kinase, a functional receptor for glial cell line-derived neurotrophic factor (GDNF). Multiple sequence alignments of seven vertebrate sequences and one invertebrate RET sequence delineated four distinct N-terminal domains, each of about 110 residues, containing many of the consensus motifs of the cadherin fold. Based on these alignments and the crystal structures of epithelial and neural cadherins, we have generated molecular models of each of the four cadherin-like domains in the extracellular region of human RET. The modeled structures represent realistic models from both energetic and geometrical points of view and are consistent with previous observations gathered from biochemical analyses of the effects of Hirschsprung's disease mutations affecting the folding and stability of the RET molecule, as well as our own site-directed mutagenesis studies of RET cadherin-like domain 1. We have also investigated the role of Ca(2+) in ligand binding by RET and found that Ca(2+) ions are required for RET binding to GDNF but not for GDNF binding to the GFRalpha1 co-receptor. In agreement with these results, RET, but not GFRalpha1, was found to bind Ca(2+) directly. Our results indicate that the overall architecture of the extracellular region of RET is more closely related to cadherins than previously thought. The models of the cadherin-like domains of human RET represent valuable tools with which to guide future site-directed mutagenesis studies aimed at identifying residues involved in ligand binding and receptor activation.

C-cell and thyroid epithelial tumours and altered follicular development in transgenic mice expressing the long isoform of MEN 2A RET

Gain-of-function mutations in the gene encoding the receptor tyrosine kinase RET have been identified as the aetiological factor for multiple endocrine neoplasia type 2A (MEN2A). MEN2A is a dominantly-inherited cancer predisposition syndrome characterized by medullary thyroid carcinoma, a tumour of the calcitonin-producing thyroid C-cells. There are three isoforms of RET: RET9, RET43 and RET51, and although in vitro evidence suggests they vary in cellular transformation activities, little is known about their function in tumorigenesis in vivo. To address this, we used RET51 cDNA to construct mice in which the most frequent MEN2A mutation, Cys-634-Arg, was expressed under the control of the human calcitonin promoter (CT-2A mice). These mice developed C-cell tumours resembling human MTC and follicular tumours resembling human papillary thyroid carcinoma (PTC) depending on the founder line examined. One founder line developed compound MTC/PTC at low frequency (8%) and pancreatic cystadenocarcinoma. CT-2A mice also displayed a developmental defect in thyroid follicular structure, in which much of the thyroid was occupied by large irregular cystic follicles thought to be derived from the ultimobranchial body, a developmental precursor of the thyroid gland. The CT-2A mice will provide a suitable model to further study the effects of the MEN 2A RET mutation in vivo.

RET/PTC rearrangements in thyroid nodules: studies in irradiated and not irradiated, malignant and benign thyroid lesions in children and adults

Rearrangements of the RET proto-oncogene may occur in both naturally occurring and radiation-induced papillary thyroid carcinomas. Conflicting results on the frequency and type of RET/PTC rearrangements have been reported in relation to age, radiation exposure, and histological tumor variant. We designed the present study to evaluate in a single laboratory, using the same methodologies, the pattern of RET/PTC activation in thyroid tumors from different groups of patients (exposed or not exposed to radiation, children or adults, with benign or malignant tumors) in relationship to the above mentioned variables. We studied 154 patients with benign nodules (n = 65) or papillary thyroid cancer (n = 89). In the last group, 25 were Belarus children exposed to the post-Chernobyl radioactive fallout, 17 were Italian adults exposed to external radiotherapy for benign diseases, and 47 were Italian subjects (25 children and 22 adults) with no history of radiation exposure. Among patients with benign thyroid nodules, 21 were Belarus subjects (18 children and 3 adults) exposed to the post-Chernobyl radioactive fallout, 8 were Italian adults exposed to external radiation on the head and neck, and 36 were Italian adults with naturally occurring benign nodules. The overall frequency of RET/PTC rearrangements in papillary thyroid cancer was 55%. The highest frequency was found in post-Chernobyl children and was significantly higher (P = 0.02) than that found in Italian children not exposed to radiation, but not significantly higher than that found in adults exposed to external radiation. No difference of RET/PTC rearrangements was found between samples from irradiated (external x-ray) or not irradiated adult patients, as well as between children and adults with naturally occurring, not irradiated, thyroid cancer. When analyzing the type of RET/PTC rearrangement (RET/PTC1 or RET/PTC3), no major difference was apparent. In addition, eight cases with an unknown RET/PTC rearrangement and three cases with the concomitant expression of RET/PTC1 and RET/PTC3 were found. No significant correlation was observed between the frequency and/or the type of RET/PTC rearrangement and clinical-epidemiological features of the patients such as age at diagnosis, age at exposure, histological variant, gender and tumor-node-metastasis (TNM) categories. RET/PTC rearrangements were also found in 52.4% of post-Chernobyl benign nodules, in 37.5% of benign nodules exposed to external radiation and in 13.9% of naturally occurring nodules (P = 0.005, between benign post-Chernobyl nodules and naturally occurring nodules). The relative frequency of RET/PTC1 and RET/PTC3 in rearranged benign tumors showed no major difference. In conclusion, our results indicate that the presence of RET/PTC rearrangements in thyroid tumors is not restricted to the malignant phenotype, is not higher in radiation-induced tumors compared with those naturally occurring, is not different after exposure to radioiodine or external radiation, and is not dependent from young age. Other factors, probably influenced by ethnic or genetic background, may act independently from or in cooperation with radiation, to trigger the DNA damage leading to RET proto-oncogene activation.

Genetic markers in thyroid neoplasia

Cancer is a disease of genes. Detection of genetic abnormalities associated with cancers of various cell types can now be used for genetic counseling, diagnosis or treatment selection. In the case of thyroid cancer, genetic testing for mutations of the RET oncogene has had a profound effect on the management of medullary thyroid carcinomas. There is also considerable information on the genetic changes associated with development and progression of cancers of thyroid follicular cells, although these have not yet proven to be of practical value for clinical diagnosis or to guide prognosis and therapy.

New reciprocal translocation t(6;10) (q27;q11) associated with idiopathic myelofibrosis and eosinophilia

Idiopathic myelofibrosis (IM), is a chronic myeloproliferative disorder (MPD) characterised by marrow fibrosis, extramedullary haematopoiesis and a leuco-erythroblastic picture of the peripheral blood. Cytogenetic data of IM is scarce: no specific karyotypic anomalies have been yet described. Trisomy 1q, del(13q), del(20q) and trisomy 8, appear in two-thirds of the cases with chromosome aberrations. We report on a 41-year-old patient diagnosed with IM associated with eosinophilia, bearing a novel translocation t(6;10)(q27;q11) as the sole chromosome anomaly. The patient, progressed to AML-M5a within 18 months from diagnosis. Recently new specific chromosomal translocations have been described in chronic MPD. These findings have allowed the classification of new syndromes with defined molecular abnormalities. The case we describe, because of the peculiar clinical features and the association with a previously unreported chromosomal translocation, might be a noteworthy addition.

RET proto-oncogene mutation in a mixed medullary-follicular thyroid carcinoma

A case of a patient with an uncommon thyroid carcinoma, showing histological and immunohistochemical features of both follicular and parafollicular cells is described. Somatic point mutation (ATG to ACG heterozygotic mutation at codon 918) of the RET proto-oncogene was detected in tumor tissue, as confirmed by immunohistochemical expression of RET oncoprotein. Our findings suggest that constitutive RET proto-oncogene activation may be involved in the development of mixed medullary-follicular thyroid carcinoma.

Signaling complexes and protein-protein interactions involved in the activation of the Ras and phosphatidylinositol 3-kinase pathways by the c-Ret receptor tyrosine kinase

Proximal signaling events and protein-protein interactions initiated after activation of the c-Ret receptor tyrosine kinase by its ligand, glial cell line-derived neurotrophic factor (GDNF), were investigated in cells carrying native and mutated forms of this receptor. Mutation of Tyr-1062 (Y1062F) in the cytoplasmic tail of c-Ret abolished receptor binding and phosphorylation of the adaptor Shc and eliminated activation of Ras by GDNF. Phosphorylation of Erk kinases was also greatly attenuated but not eliminated by this mutation. This residual wave of Erk phosphorylation was independent of the kinase activity of c-Ret. Mutation of Tyr-1096 (Y1096F), a binding site for the adaptor Grb2, had no effect on Erk activation by GDNF. Activation of phosphatidylinositol-3 kinase (PI3K) and its downstream effector Akt was also reduced in the Y1062F mutant but not completely abolished unless Tyr-1096 was also mutated. Ligand stimulation of neuronal cells induced the assembly of a large protein complex containing c-Ret, Grb2, and tyrosine-phosphorylated forms of Shc, p85(PI3K), the adaptor Gab2, and the protein-tyrosine phosphatase SHP-2. In agreement with Ras-independent activation of PI3K by GDNF in neuronal cells, survival of sympathetic neurons induced by GDNF was dependent on PI3K but was not affected by microinjection of blocking anti-Ras antibodies, which did compromise neuronal survival by nerve growth factor, suggesting that Ras is not required for GDNF-induced survival of sympathetic neurons. These results indicate that upon ligand stimulation, at least two distinct protein complexes assemble on phosphorylated Tyr-1062 of c-Ret via Shc, one leading to activation of the Ras/Erk pathway through recruitment of Grb2/Sos and another to the PI3K/Akt pathway through recruitment of Grb2/Gab2 followed by p85(PI3K) and SHP-2. This latter complex can also assemble directly onto phosphorylated Tyr-1096, offering an alternative route to PI3K activation by GDNF.

RET proto-oncogene mutations in thyroid carcinomas: clinical relevance

Different forms of RET mutations are found in papillary and medullary thyroid carcinomas. Rearrangements with other genes (RET/PTC oncogene) play a causative role in a significant proportion of papillary thyroid carcinomas. In this case, several factors influence the frequency and the type of RET/PTC, such as exposure to radiation, age and histological variant of the papillary tumor. On the other hand, the presence of the mutation does not seem to influence the biological behavior of the tumor or its response to conventional treatment modalities. In the setting of medullary thyroid cancer, germline RET point-mutations are implicated in the pathogenesis of virtually all hereditary forms and somatic point-mutations in nearly half of the sporadic forms. The clinical impact of this finding is that family members at-risk of hereditary MTC may be screened by genetic analysis, to distinguish those carrying or not-carrying the mutation. The last can be reassured on their status and relieved from further follow-up. Those with the mutation may be treated at a pre-clinical stage of the disease or even before the disease is started. The present review is focused on the clinical implication of RET gene mutations in thyroid cancer patients.